“Join me on Team ‘18,” Barack Obama wrote in a recent fundraising email from his old political group, Organizing for Action. “Every election, every ballot measure, every conversation between now and November … it all matters.”

It wasn’t much, but the email was one of Obama’s few public, political, overtly partisan appeals as the Democratic Party approaches midterm elections that could stop President Trump’s agenda and boost Democratic prospects going into 2020. To have an ex-president who remains highly popular with his party sitting on the sidelines cannot be what Democrats hoped.

There are reports that Obama plans to campaign for some Democrats starting in September. But beyond simply hitting the stump for the midterms, Obama could be, if not the full-fledged leader of the Resistance, at least a constant and public critic of the direction taken by the Trump administration and Republicans in Congress.

Instead, Obama isn’t seen much. At the end of July, he and former Vice President Joe Biden made a stir when they dropped by a Washington, D.C., bakery for sandwiches. The visit had a purpose — the shop, Dog Tag Bakery, helps disabled veterans and their families — but besides shaking hands and posing for selfies, Obama didn’t do anything that could be construed as politicking.

Obama did have a political message earlier in July, but he chose to deliver it in South Africa, thousands of miles away from U.S. midterm campaigning. Speaking at an event in Johannesburg honoring Nelson Mandela, Obama never mentioned Donald Trump’s name, but his message was undoubtedly aimed at his successor in the White House.

“Look around,” Obama said. “Strongman politics are ascendant suddenly, whereby elections and some pretense of democracy are maintained — the form of it — but those in power seek to undermine every institution or norm that gives democracy meaning.

“We see the utter loss of shame among political leaders,” Obama continued, “where they’re caught in a lie and they just double down and they lie some more.”

Obama’s speech got some coverage and some nostalgic comments by Democrats. But at the same time, President Trump is ramping up his political travel, headlining rallies just in the last week in the key states of Florida, Pennsylvania and Ohio — a combination of 2018 politicking for Republicans and 2020 politicking for himself.

A quick visit to a bakery is not quite the same.

There is no leader of the Democratic Party. A president is the leader of the party in the White House, and the opposition party doesn’t really have a leader. For Democrats today, who would it be? Charles Schumer? Nancy Pelosi? One of the party’s 2020 hopefuls? There just isn’t one.

For Democrats, Obama, who isn’t running for anything, could be as close to a leader as an out-of-power party can have until the Democrats’ next presidential nominee comes along. But he’s just not taking the job.

In June, New York magazine published an article with the almost plaintive headline, “Where is Barack Obama?” Writer Gabriel Debenedetti portrayed a former president who, for whatever reason, has decided not to stay up on day-to-day politics, focusing instead on the new Obama Foundation and on his memoirs.

“In private conversations, Obama rarely mentions Trump at all,” Debenedetti reported. “Those who’ve visited the office he’s leased from the World Wildlife Fund in Washington’s West End say he’s eager to talk for hours about the world’s ills. When informed about the latest presidential tweetstorms aimed at him, he chuckles and changes the subject.”

Debenedetti talked to Obama friends who marveled at the former president’s “Zen-like” calm in the face of the Trump tumult. That, of course, was a phrase often used to describe Obama in the White House, too.

Maybe that works for him. But for his admirers — and many Democratic voters — Obama’s absence borders on the mysterious.

“How did the most ubiquitous man in America for eight years virtually disappear?” Debenedetti asked. “What explains his near absence from the political stage, where he might argue publicly against the reversals of his policy accomplishments, and also from American life more broadly?”

What could Obama do for Democrats this November? There are certainly states and districts in which candidates would welcome an appearance. But probably more important, he could travel the country raising millions and millions of dollars for Democratic candidates. For that job, the only thing better than an ex-president is a sitting president, and Democrats don’t have one of those now.

Actually, one Obama is doing some shoe-leather work for the midterms. This week came news that former first lady Michelle Obama will travel around the country in a weeklong voter registration effort in late September.

That will certainly be welcome in many Democratic circles. But at the same time, no one should be surprised if party activists ask Mrs. Obama: “Where is your husband?”

— Byron York is chief political correspondent for The Washington Examiner.